|Glass ceramics produced following a precisely controlled temperature regimen end up with nanocrystals 100 nm in size or less. (Credit: Jan-Peter Kasper/FSU)|
Jena, Germany--A glass ceramic with a nanocrystalline structure developed at the Otto-Schott-Institute for Glass Chemistry has both the high strength and the proper optical characteristics for use in dentistry.1 Previous ceramics were not strong enough for dental use and also were not translucent enough, giving the impression of teeth made out of plaster.
Teeth endure a higher stress than any other component of the human body; any ceramic useful for dentures, inlays, or bridges would have to approach the strength of natural tooth enamel. But relatively strong microcystalline ceramics contain crystals large enough to strongly scatter light, giving rise to that unwanted plaster-teeth effect. However, high-density ceramics previously developed by the Jena group for use in computer hard drives can be modified to produce a translucency similar to natural teeth (as well as the proper degree of whiteness).
"We achieve a strength five times higher than with comparable denture ceramics available today," says Christian Rüssel of the Friedrich Schiller University Jena.
To achieve these characteristics, the glass ceramics are produced according to a precisely specified temperature scheme: first the basic materials are melted at about 1500 °C, then cooled down and finely cut up. Then the glass is remelted and cooled down again. Finally, nanocrystals are generated by controlled heating to about 1000 °C. "This procedure determines the crystallization crucial for the strength of the product," says Rüssel. But this was a technical tightrope walk, as too much crystallization produced the plaster effect. The secret of the Jena glass ceramic lies in the fact that the nanocrystals are at most 100 nm in size.
1. M. Dittmer and C. Rüssel, J. Biomed. Mater. Res. B Appl. Biomater. (2011); doi: 10.1002/jbm.b.31972